1. Field of the Invention
The present invention relates to a joint restraint for connecting a pair of axially aligned pipes and/or appurtenances such that a tight fit and suitable seal are formed therebetween, and such that protection is provided against the disengagement that could occur when force is applied in the axial direction.
2. Description of Related Art
It is known to employ a joint restraint to prevent disengagement of axially aligned pipes and/or appurtenances. For purposes of this application, pipes and/or appurtenances shall be referred to herein collectively as "pipes" or in the singular as "pipe". Typically, a joint restraint comprises an annular body from which a plurality of evenly spaced wedge housings axially extend. The annular body encircles the outer surface of a first pipe, and is engaged therewith using actuatable wedges held within each of the wedge housings. The annular body is also connected to an integral flange disposed at the terminus of a second pipe, so as to hold the first and second pipes together.
Examples of joint restraints, the pipes with which they function and associated equipment may be found in U.S. Pat. No. 4,092,036 to Sato et al. ("Sato '036"), U.S. Pat. No. 5,071,175 to Kennedy, Jr. ("Kennedy '175"), and U.S. Pat. No. 5,544,922 to Shumard et al. ("Shumard '922"), the entire disclosures of which are incorporated herein by reference.
Joint restraints used in the past have suffered from several disadvantages that have diminished their functionality and ease of use, and that have resulted in increased manufacturing costs. For example, many joint restraints employed in the past required the use of sand cores in casting the wedge housings. Because the use of such sand cores increases processing time and expense, it is desirable to employ a design that minimizes or eliminates the need for such sand cores.
Another disadvantage of joint restraints employed in the past is diminished or unpredictable performance with plastic pipe (e.g., PVC). Many joint restraints rely on friction between a gripping surface or mechanism such as wedges, wedge rings and serrated split rings and the pipe surface to secure the pipe. However, the behavior of such friction-based means is unpredictable when used with PVC, and the friction force that may be induced is limited.
The Kennedy '175 joint restraint addresses this problem by employing a wedge having pipe-engaging teeth that may be driven into engagement with the pipe surface. The Kennedy '175 joint restraint, however, has several disadvantages. Specifically, the design requires the use of sand cores in casting, the design lacks a reliable method of keeping the wedge in place and the wedge does not retract when the actuating screw is retracted.
The Kennedy '175 disclosure contemplates the use of a twist-off bolt to reduce the possibility of preventing the wedge from being over-torqued during initial actuation. Ideally, however, the wedge itself should resist further intrusion into the pipe surface after the initial actuation groove is formed.
Another disadvantage of conventional joint restraints is their lack of flexibility. For example, in the Kennedy '175 patent, once the joint restraint is installed on the pipe, the position of the wedges is fixed, other than a relatively minor amount of radial play, with respect to their respective wedge housings. It is desirable to allow the wedges some freedom to move within their respective housings independently of the joint restraint in order to increase the capacity of the system to accommodate joint deflection resulting from settlement or other force on the pipes. Likewise, it is advantageous to allow some play in the radial displacement of an installed wedge in order to accommodate greater variations in pipe size without the need for shims or spacers.
Yet another disadvantage of conventional joint restraints is the typical lack of means for retaining wedges or other restraint means in their respective housings prior to installation in the field. Such retaining means are desirable in order to allow preassembly of wedges into a joint restraint, and to reduce the likelihood of subsequent wedge loss.
A need exists, therefore, for a simple and robust joint restraint that provides reliable restraint, that minimizes the use of cores in molding, that is easy to assemble, install and use, and that is multi-functional and flexible with respect to pipe size and type. Such a device should also provide a mechanism for retaining wedges in their housings prior to or after installation.